Obesity is a disease of energy imbalance, when energy input is more than output. Excess energy is stored in the form of triglycerides (TGs) in the adipose tissue. Increased adipose cell size causes hypertrophic obesity and increased cell number causes hyperplastic obesity characteristic of a more severe condition. The key causes of obesity are the increased consumption of energy-rich but nutrient-poor diets (like saturated fats and sugars) and reduced physical activity. 65% of the US population is overweight, where body mass index (BMI) is greater than 25 and approximately 25% of them are obese, having BMI>30. The prevalence of obesity has increased dramatically over the last decade. Obesity leads to increased risk of chronic diseases such as type 2 diabetes, insulin resistance, hypertension, stroke, cardiovascular diseases, respiratory problems, gallbladder disease, osteoarthritis, sleep apnea and certain cancers (Expert Opin. Ther. Targets, 2009, 13, 2, 195-207). The increasing evidence that severe obesity has a genetic basis, resulting in maintaining and defending an elevated weight, may explain why long-term weight loss is very difficult to achieve. This has strengthened the argument that severe obesity should be treated with pharmacological agents along with conventional diet and exercise regimes.
Diacylglycerol acyltransferase (DGAT) is an enzyme that catalyses the biosynthesis of triglyceride at the final step of the process, converting diacylglycerol (DAG) and fatty acyl-coenzyme A (CoA) into triglyceride. The enzymatic activity is present in all cell types because of the necessity of producing triglyceride for cellular needs. The amount of triglyceride synthesized varies from cell to cell, with the adipocytes, hepatocytes and intestinal enterocytes producing much more triglyceride, for storage or incorporation into lipoproteins, than other cell types. Because of its critical role in the biosynthesis of triglyceride, a neutral lipid that is the densest form of energy storage in animals, alteration of the expression and/or activity of DGAT in any of the tissues or organs would be expected to perturb the systemic energy metabolism. Diacyl glycerolacyltransferase 1 (DGAT1) is one of two known DGAT enzymes that catalyze the final step in triglyceride synthesis. Although most tissues generate triacylglycerols, DGAT1 is known to be highly expressed in the intestine and adipose with lower levels in the liver and muscle. Inhibition of DGAT1 in each of these tissues (intestine, adipose, liver and muscle) would inhibit triacylglycerol synthesis and may reverse the pathophysiology of excessive lipid accumulation in human metabolic disease.
Inhibitors of varying structural types of DGAT1 have been reported to be potential agents for the treatment for obesity and other disorders. The particular interest in DGAT1 inhibition stems from the reported phenotype of DGAT1 deficient (Dgat1−/−) mice. These animals are viable, resistant to weight gain when fed a high-fat diet, and show increased insulin and leptin sensitivity (Nature Genetics, 2000, 25, 87-90). Resistance to weight gain results from increased energy expenditure rather than decreased food intake (the animals are in fact hyperphagic) and is associated with loss of adipose rather than lean tissue mass. Most aspects of this phenotype can be reproduced in rodents by treatment with a potent and selective small molecule inhibitor of DGAT1.
XP620 (BMS) has been reported to be a selective DGAT1 inhibitor, which is able to block DGAT1 mediated retinyl-ester formation in Caco-2 cells. The potency against DGAT1 was in the order of 100 nM with no activity against DGAT2. Other small-molecule inhibitors reported are aryl alkyl acids from Bayer, phosphonic acid diesters from Otsuka, substituted ureas from Sankyo, pyrrolo[1,2-b]pyridazine derivatives from Tularik (now Amgen) and oxadiazoles from AstraZeneca (Expert Opin. Ther. Targets, 2006, 10, 5, 749-757). The PCT publication, WO2007016538 discloses biphenyl amino acid derivatives, and pharmaceutical salts and esters, thereof that have utility in the inhibition of DGAT1 and in the treatment of obesity and related diseases. The PCT publication, WO2009040410 discloses oxadiazolyl substituted benzimidazole and indole derivatives useful for treating conditions or disorders associated with DGAT1 activity in animals, particularly humans. However to date, there is an unmet medical need for effective and safe pharmacotherapy for obesity thus leaving a significant challenge to pharmaceutical industry.